AUTHOR=Barke Birthe H. , Daubert Mareike , Hörandl Elvira 

TITLE=Establishment of Apomixis in Diploid F2 Hybrids and Inheritance of Apospory From F1 to F2 Hybrids of the Ranunculus auricomus Complex

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01111

DOI=10.3389/fpls.2018.01111

ISSN=1664-462X

ABSTRACT=<p>Hybridization and polyploidization play important roles in plant evolution but it is still not fully clarified how these evolutionary forces contribute to the establishment of apomicts. Apomixis, the asexual reproduction via seed formation, comprises several essential alterations in development compared to the sexual pathway. Furthermore, most natural apomicts were found to be polyploids and/or hybrids. The <italic>Ranunculus auricomus</italic> complex comprises diploid sexual and polyploid apomictic species and represents an excellent model system to gain knowledge on origin and evolution of apomixis in natural plant populations. In this study, the second generation of synthetically produced homoploid (2<italic>x</italic>) and heteroploid (3<italic>x</italic>) hybrids derived from sexual <italic>R. auricomus</italic> species was analyzed for aposporous initial cell formation by DIC microscopy. Complete manifestation of apomixis was determined by measuring single mature seeds by flow cytometric seed screen. Microscopic analysis of the female gametophyte formation indicated spontaneous occurrence of aposporous initial cells and several developmental irregularities. The frequency of apospory was found to depend on dosage effects since a significant increase in apospory was observed, when both F<sub>1</sub> parents, rather than just one, were aposporous. Other than in the F<sub>1</sub> generation, diploid <italic>Ranunculus</italic> F<sub>2</sub> hybrids formed B<sub>III</sub> seeds and fully apomictic seeds. The results indicate that hybridization rather than polyploidization seems to be the functional activator of apomictic reproduction in the synthetic <italic>Ranunculus</italic> hybrids. In turn, at least two hybrid generations are required to establish apomictic seed formation.</p>